1. Field of the Invention
The present invention relates to optical components and in particular a twin guide amplifier which can be used as either a 1.times.2 optical switch, or a 2.times.1 optical combiner with low or zero loss.
2. Related Art
Optical components of this type can be used as elements in optical telecommunications systems. A 1.times.2 optical switch is capable of directing an optical input from one port to a selected one of two output ports. A 2.times.1 optical combiner is capable of combining optical inputs from two ports to provide a single optical output from the remaining port.
Electromagnetic radiation used in optical communications normally lies either in the near infra-red or visible region of the spectrum. The terms optical and light should not, therefore, be interpreted in this specification as implying a limitation to the visible region of the electromagnetic spectrum.
The energy of semi-conductor bandgaps in this specification are expressed in terms of the wavelength of electromagnetic radiation having a quantum energy equal to the bandgap energy, i.e. capable of raising a current carrier over the bandgap.
Optical components of the type with which this invention is concerned are formed on semi-conductor substrates by techniques similar to those used for production of integrated electronic components. Such components are frequently referred to as integrated optical components. Many different forms of integrated optical components are known, for example as described in European Patent Application 0241143, European Patent Application 89302355.6 and UK Patent Application 8920435.8. In general the techniques for fabricating integrated optical components described in these documents are applicable to the present invention.
Other known devices include integrated laser amplifiers and passive waveguide splitters, as described in "Proposals and Analyses on Laser Amplifier Based Integrated Optical Circuits" K Otsuka, 1981 IEEE Jnl of Quantum Electronics, Vol EQ-17, No.1, Pages 23-28 in which an integrated optical component includes an amplifier and splitter which are separated.
"Guided-wave Optical Gate Matrix Switch", M Kobayashi, ECOC 1985, Post-deadline Digest, pages 73-76 describes a 4.times.4 matrix switch in which a laser amplifier is inserted for gating and amplification. In this component the splitter and gain blocks are separate and the device has an overall loss of 22 dB and crosstalk less than -13 dB. The individual gates and combiner has a 12 dB loss and less than -18 dB crosstalk.
"InGaAsP/InP Monolithic Integrated Circuit with Lasers and an Optical Switch"--S Sakano, H Innoe, H Nakamura, et al, 1986, Electronic Letters, Vol 22, No.11, pages 594-596 describes a 2.times.2 carrier injection optical switch with no gain with a laser at each of the two input ports and a laser amplifier at each output port of the switch. Again the switch and amplifier are separate, carrier injection is used to alter the refractive index but does not provide gain. This device achieves crosstalk of less than 13 dB.
Other devices are described in the following papers:
"Monolithic LD Optical Matrix Switches", M Ikeda, O Ohguchi, K Yoshino, ECOC 1987, Vol 1, Page 227-230.
"Optical Amplification by Monolithically Integrated Distributed-Feedback Lasers", H Inoue and S Tsuji, 1987, Applied Physics Letters, Vol 51, No.20, Pages 1577-1579.
"Optical Self-Routing Switch using Integrated Laser Diode Optical Switch", R Kishimoto and M Ikeda, 1988, IEEE Jnl on Sel. Areas in Communication, Vol 6, No.7, Pages 1248-1254.
"Tunable MQW-DBR Laser with Monolithically Integrated GaInAsP/InP Directional Coupler Switch", F Hernandex-Gil, et al, 1989, Electronic Letters, Vol 25, No.19, Pages 1271-1272.
"Widely Tunable Y-coupled cavity integrated Interferometric Injection Laser", Schilling et al, Electronic Letters 26 1990 (4) 243.
G. Muller et al. Electronic Letters 26 1990 (2) 115.
A successful optical switch must have low crosstalk and low or zero loss. The prior art referred to above has, as a common feature, separation of the amplification or active sections of the component from the coupling sections and is characterised by mediocre crosstalk performance.